The present invention relates to a process for the preparation of organosilicon-disulfanes.
Organosilicon-disulfanes are employed in the production of rubber articles containing silica as a filler. The use of organosilicon-disulfanes of high purity is of particular interest in this field of technology (EP-A 0 732 362; L. Panzer, American Chem. Soc., Rubber Div. Meeting 1997).
The preparation of organosilicon-disulfanes of high purity is difficult for the expert, because known processes, such as, for example, the reaction of 3-chloropropyltriethoxysilane with Na.sub.2 S.sub.2, lead to product mixtures with contents of monosulfane or long-chain oligosulfanes. These contents are undesirable, however, because monosulfane is inactive in the application, and the long-chain oligosulfanes lead to undesirable effects in the mixing processes.
It is known to prepare organosilicon-disulfanes of high purity by disulfurizing polysulfanes with cyanides, phosphanes or sulfites (EP-A 0 773 224).
This process has the disadvantage that a polysulfane must first be prepared, which is then degraded to the disulfane. Another disadvantage is the use of toxic substances such as cyanides and such as phosphanes.
It is furthermore known to prepare organosilicon-disulfanes by oxidizing the corresponding mercaptosilanes by means of MnO.sub.2 or SO.sub.2 Cl.sub.2 (EP-A 0 718 392; DE-A 23 60 470).
The known processes have the disadvantage that a mercaptosilane is employed as an educt, which must be prepared by an industrially involved process from the corresponding chloroalkylsilanes and thiourea, with subsequent cleavage of the thiruronium salt.
It is therefore an object of the present invention to avoid the disadvantages and shortcomings of the prior known technology.